After reading a post on The
Cafes about the lack of dynamics in the CSS language, I found myself inspired
to do something about it. It became clear that something had to be done and that we
couldn’t wait for the W3C to come up with a new standard and browser vendors to incorporate
them.
There were two things I wanted to enrich the CSS language with:
To make it work, I created an HttpHandler for ASP.NET that is able to parse these
two new features and apply them to the stylesheet. It does not interfere with any
CSS standards because everything is handled by the server.
Here is an example of a .css file that uses these new capabilities.
define BACKCOLOR = #00FFFF;
define FORECOLOR = pink;
define TOTALWIDTH = 550;
define RIGHTWIDTH = browser == "IE" & version >= 6 ? "150px" : "170px";
define LEFTWIDTH = TOTALWIDTH / 2 + "px";
body{
background-color: BACKCOLOR;
color: FORECOLOR;
width: TOTALWIDTHpx;
}
#RightColumn{
width: RIGHTWIDTH;
}
#LeftColumn{
width: LEFTWIDTH;
}
This will then be outputted as this standard compliant stylesheet:
body{
background-color: #00FFFF;
color: pink;
width: 550;
}
#RightColumn{
width: 150px;
}
#LeftColumn{
width: 275px;
}
All the lines beginning with "define" will be treated as a variable declaration, parsed
and then deleted from the parsed stylesheet. Notice the two variable names "browser"
and "version". Those two variables are built in properties that return the browser
name and major version number respectively.
The scripting syntax is 100% C# because it is compiled by the CodeDom into C# code
in-memory. No new syntax of any kind is invented. The reason to use C# and not VB.NET
is that developers or designers writing stylesheets probably also know JavaScript
which also uses the C style syntax like C#. So, if you are comfortable writing JavaScript, it should be no problem to add scripting to the new CSS variables.
Remember, like JavaScript, these features are case-sensitive. However, that is not
why the variable names are upper cased, I just thought it makes sense to let them
stick out from the rest of the styles.
Implementation
There are two versions of the HttpHandler – one to use if you can control the IIS
and one if you can’t.
If you are able to let the IIS send .css files to the ASP.NET engine you should download
the CssHandler.cs file below and add it to the App_Code folder and then add the following
to the web.config:
<httpHandlers>
<add type="CssHandler" verb="*" path="*.css" />
</httpHandlers>
If you can’t access the IIS, you need to download the CssHandler.ashx below and then
call that file while passing the .css file as a query string in the URL like this:
<link rel="stylesheet" type="text/css" href="csshandler.ashx?path=style.css" />
Total feature list
This is the total feature list of the handler:
- Add variables to CSS (feature)
- Use scripting capabilities (feature)
- Server and client side caching (performance)
- Cache dependant of the source .css file (performance)
- Whitespace and comment removal (performance)
- Works only on .css files (security)
- Blocks the System namespace (security)
Word of caution
Because the scripting language is pure C#, it also means that you have to take injection
attacks into account. I’ve already made sure that any scripting using anything in
the System namespace will be rejected. That means that you can’t use any System.File.IO
commands or anything else that has the word “System.” in it. That eliminate probably
99% of the obvious attack surface, but it is not totally secure.
Download
CssHandler
(.cs - for IIS access).zip (1,96 KB)
CssHandler
(.ashx - for non IIS access).zip (1,91 KB)
* $4.95/month BlogEngine.net Hosting – Click Here!